Burberry chief executive Angela Ahrendts is to take up her new post as head of Apple's retail empire next week, raising the prospect that she could forfeit an £8m bonus.

The British fashion label originally warned investors that Ahrendts could start her job at Apple by mid-2014, with the company suggesting she was likely to stay on to collect two major share awards that are due to mature on 6 June.

But on Wednesday night, announcing Apple's financial results, chief executive Tim Cook said he was "looking forward to welcoming our new retail and online leader Angela Ahrendts, who will be joining Apple's executive team next week". The news led to confusion in London, with Burberry declining to confirm the date of her departure to investors.

The label's design boss Christopher Bailey is chief executive in waiting, but no announcement has been made to the London Stock Exchange confirming the change.

The delay suggests negotiations over a settlement for Ahrendts are going to the wire. It is understood an announcement will be made when Burberry's board has reached a decision.

The American executive, who oversaw Burberry's transformation from a smart rainwear company into a sought-after international fashion label, is returning to her homeland after nine years in London.

She resigned in October and has now completed a six-month notice period. In June she would be due to collect shares worth more than £7.6m at today's £14.42 share price.

Apple declined to comment on whether it had offered to compensate Ahrendts for any loss of bonus, but her financial rewards at the world's biggest technology company are likely to be generous.

She will be the only female member of the Californian company's 10-strong leadership team but will not have a seat on the main board, where Cook is the only executive director.

When in 2012 Cook recruited former Dixons boss John Browett to run his retail arm, the British executive was handed a golden hello of 100,000 Apple shares, worth $57m at the time. These were due to vest over a five-year period, but Browett's stay at Apple was brief.

He left the company after six months, and collected 5,000 shares from the original award – but at $610 apiece he walked away with $3m.

Ahrendts will have a wider remit than her predecessor, overseeing more than 420 high street stores in 15 countries and online sales via the Apple website, which retails in 39 countries.

Apple's pared back, steel-and-glass shops had more in common with art galleries than with the overflowing electronics outlets found on most high streets when they first appeared in 2001. They earn more per square foot than any other retail chain in the world, but have in effect been leaderless since 2011, when Browett's predecessor Ron Johnson left for US group JC Penney after building up Apple's retail presence during his 11-year tenure.

Despite a vacuum at the top, Apple stores earned a record $7bn (£5bn) in the first quarter of this year, an increase of 9% on the same period last year. They attracted 114m visitors during the quarter, about 21,000 visitors per store, per week.